I found a cheap solution online in a photo. One of those plastic dome covers meant for outside garden hose spigots. I cut off the rubber tightener, sealed the hole on the end, and then used a scissors to cut about a two inch gap on one flat side. Plug in the cable and then place the cover over it and it flexes enough to wedge it in. I also use the little luggage lock from my Clipper Creek so that's protected from the elements too. Worked great recently in an overnight snowfall. At some point I'll probably paint it black to match the car.
If anyone knows a Maker on Etsy.com I'm sure they could craft something custom given some dimensions and photos, if they don't have access to a Bolt.
2017 Bolt EV Premier